Revving your big block

[blykins]

You have to qualify this into two categories.....what the rotating assembly can handle and what the engine as a whole can handle.

For example, a rotating assembly could potentially turn 7000 rpm without issue because of the rod design, piston design, etc. However, due to the cylinder head, compression, and camshaft, it may only make peak hp at 5000 rpm.

Looking at the opposite, you may see someone put a big set of cylinder heads and a huge cam into an engine with factory rods, cast pistons, etc. In that scenario, the bottom end may be able to handle 6000 rpm, but the heads and the camshaft want 7000.

As an aside, one of the BIGGEST fallacies hopping around the internet engine forums is that a long stroke engine can't turn high rpms. I get very tired of hearing that big blocks with long stroke crankshafts are slow revvers, or can't turn higher rpms, but a small block is very zippy and can spin to the moon if necessary.

There are so many variables involved, that a blanket statement like such simply can not be made.

[DanEC]

Originally Posted by blykins

As an aside, one of the BIGGEST fallacies hopping around the internet engine forums is that a long stroke engine can't turn high rpms. I get very tired of hearing that big blocks with long stroke crankshafts are slow revvers, or can't turn higher rpms, but a small block is very zippy and can spin to the moon if necessary.

There are so many variables involved, that a blanket statement like such simply can not be made.

I used to subscribe to this idea that long strokes killed revs, but I started to have doubts when I bought my 2003 Lightning with the 5.4 modular motor that is about as undersquare as you can get. Then I bought a Coyote engine Mustang GT, which again is undersquare and zings towards it's 7000 rpm redline like no body's business. That pretty much killed the myth for me. Also, my 4.25 stroke FE seems to rev just as strong as my 3.75 stroke Chev 427 - well, at least up to a point.

[blykins]

Horsepower/torque is one of the biggest factors there.

Most of your Mountain Motor and some of your Pro Stock engines use extremely long strokes.....like 5.5-5.75". They will zing to 8000-9000 as quick as you can get on the loud pedal.

[scottj]

Originally Posted by blykins

Horsepower/torque is one of the biggest factors there.

Most of your Mountain Motor and some of your Pro Stock engines use extremely long strokes.....like 5.5-5.75". They will zing to 8000-9000 as quick as you can get on the loud pedal.

Long stroke Pro Stock engines? I don't think anyone uses a bore smaller than 4.70" with stroke in the 3.50"-3.60" range. I think they are also using an 8.90" deck height to keep the compression height to a minimum while utilizing a shorter, lighter rod and to keep the push rods shorter. Regarding rods, I believe they are running Honda rods. They're basically BB's built to ultra-light SB specs except for the bore... so they'll rev...

[blykins]

Depends on the class...

EXTREME PRO STOCK 932 CU. IN. 2140 HP RACING ENGINE - Sonny's Racing Engines - Sonny's Racing Engines

Google some of Pat Musi's stuff and take a look at some of the mountain motor classes.

Obviously the parts are light but I'm using this as an example when people say a big block won't rev....or a long stroke won't pull rpms...

[scottj]

Originally Posted by blykins

Depends on the class...

EXTREME PRO STOCK 932 CU. IN. 2140 HP RACING ENGINE - Sonny's Racing Engines - Sonny's Racing Engines

Google some of Pat Musi's stuff and take a look at some of the mountain motor classes.

Obviously the parts are light but I'm using this as an example when people say a big block won't rev....or a long stroke won't pull rpms...

Got it... when you said "Pro Stock" I assumed you were referring to NHRA Pro Stock a.k.a. Pro Stock...

I understand your references and your point... I agree. A more accurate generality would be that lighter revs higher and accelerates quicker (engine accel) than heavier, all else being equal. Of course, when comparing SB to BB nothing else is equal... but they sure do go to extremes with the Pro Stock stuff to copy a small block rotating assembly, huh?

[blykins]

Lighter parts are certainly easier on the system. I can't imagine the piston speed of a 5.750" stroke setup at 8000 rpm.

You'd be surprised at how quick a 12.5:1, 720 hp Ford FE will rev though with a 4.250" crank....that's not really anything exotic, and the crank weighs about 70 lbs.